Motor load control



June 6, 1944. I MERCER 2,350,913

MOTOR LOAD CONTROL Filed Aug. 12, 1941 1 l r I Fwo Lowspead Rcv Hrs"spud Z: I o 2? I do If 4f 3nventor cll' ilezwn Patented June 6, 1944UNITED STATES PATENT OFFICE 2,350,913 Moron LOAD coN'rnoL John F.Mercer, Globe, am

Application August 12, 1941, Serial No. 406,567

3 Claims.

This invention relates to a device for maintaining a constant load on amotor.

In refrigerating machines at present electric motors must be designedlarge enough to start and operate the compressor when the evaporator iswarm and the back pressure is at its highest peak. During the operationof the machine the evaporator starts cooling thereby gradually reducingthe back pressure and causing the machine to pump less and less gas asthe operation continues. The head pressure at this time dropsproportionately. Finally when a desired evaporator temperature ismaintained, the motor will be running at a very light load and thus willbe very low in efficiency. However, the larger motor construction addsto the cost of the refrigerator and more current is used when the motoris started after an idle period.

It is an object of=the present invention to provide a mechanism betweenan electric motor of small proportions and a compressor for varying thespeed of the compressor while maintaining the load on the motorsubstantially constant during the various stages of the compressingperiod, means being included in the mechanism for causing the compressorto be actuated in accordance with the current required to operate themotor at a particular time.

A further object of the invention is the provision of a device formaintaining the load on a motor which operates a compressor in arefrigerating machine constant over the entire period of operation ofthe motor, means being employed for increasing or decreasing the speedof the compressor in such a manner that as the current drops in themotor circuit the compressor will automatically run fasterproportionately and vice versa.

This invention will be best understood from a consideration of thefollowing detailed description, in view of the accompanying drawingforming a part of the specification; nevertheless, it is to beunderstood that the invention is not confined to the disclosure, beingsusceptible of such changes and modifications as define no materialdeparture from the salient features of the invention as expressed in theappended claims.

In the drawing:

Figure 1 is a transverse vertical section taken along the line of Fig.5.

Figure 2 is a fragmentary end view of an electric motor and its support.

Figure 3 is a horizontal section showing the sections of a pulleyassociated in close formation.

Figure 4 is a similar horizontal section showing the sections of apulley in greater spaced relaion.

Figure 5 is a plan view of an apparatus for maintaining a constant loadon an electric motor.

Referring more particularly to the drawing, I. designates an electricmotor which is adapted to drive a compressorv of a refrigeratingmachine, or which may be adapted to drive other mechanism. This motor ispivotally mounted on a base member II by means of ears |2 rising fromthe base member and is provided with bearings I3 to receive a rod Hwhich is carried by projections l5 depending from the bottom of themotor I.

A lip l6 projects laterally from the lower portion of the motor l0 andis engaged by a spring H which is mounted on the base member Thus, itwill be seen that when a pull is exerted on the motorby a belt It thespring II will resist the tilting movement of the motor to the left asshown in Fig. 2 and thus the spring acting against the lip IE will tendto maintain the belt l8 taut.

In place of the lip l6 and the spring H the motor may be mounted on a,base member which is hinged at one end and tilted so that the weight ofthe motor will act against the belt It. The construction just describedhas not been illustrated because it is a well known form of belttightener.

A shaft 20, which is directly connected with the electric motor Ill,extends beyond one end of the motor and has a sleeve 2| slldably mountedthereon adjacent to the motor. A key 22 permits the sleeve to be movedlongitudinally of the shaft but causes the sleeve to be rotated with theshaft.

A collar 23 is rotatably mounted upon an annular shoulder 24 formedintegrally with the sleeve 2|. The numeral 25 constitutes not only abearing for the collar 23, but a thrust bearing for the sleeve 2| and islocated between the annular shoulder 24 formed on the sleeve 2| and thecollar 23. The collar 23 at diametrically opposite points carries links26 which are pivotally connected at 21 with the arms of a fork 28.

An operating arm 29, pivoted at Ill, is connected with the fork 28 sothat when the arm'is oscillated the fork will be oscillated and thesleeve 2| will be shifted towards or away from the motor III for apurpose which will be presently explained.

One section 3| of a V pulley is formed integrally with the sleeve 2|.The other section 22 of the pulley is securedat 33 to the outer end ofthe shaft 20. The section 32 is revolved with the shaft 29 as is thesection 3|, but the section 32 remains stationary with respect to thelongitudinal axis of the shaft.

The belt i3 which conforms in cross sectional area to the groove formedbetween the sections 3| and 32 of the pulley is directed to a pointwhere it engages the groove of a pulley that operates a compressor orother working element. The compressor or other working element is notshown.

A reversing motor 49 is carried by brackets 4| projecting from thehousing of the motor ID. The motor shaft which projects beyond the motor40 is provided with threads 42 which mesh with the internal threads of acollar or nut 43. This collar. shown in Fig. 1, is swivelly mounted asshown at 44 in a yoke 44' connected to the outer end of the lever or arm29. I The rotation of the shaft 42 in one direction by the motor 40causes the arm 29 to be rocked in one direction, while the reverserotation of the shaft causes the arm or lever to be moved in theopposite direction as will be presently explained. Wires 45 and 4-3 areconnected with the house current and are also connected with the motorI. The wire 45 passing through coil 41 comprises the currenttransformer. The coil 41 is connected to a secondary coil 43. The coil43 and a core 49 constitute a relay. The current in these coils will beequal and proportional to the current passing through wire 45.

The movable core 49' is plvotally connected at y 58 with a pivotallymounted switch arm 5| This switch arm is adapted to be oscillated on itspivot 52 for engaging either a contact member 53 or a contact member 54depending upon the current passing through the wire and through the coilA screw 55, having left and righthand threads has threaded connectionwith the arms 53 and 58 carrying the respective contacts 53 and 54 sothat when the screw is rotated by the thumb-piece 59 the arms 56 and'58, and likewise the respective contacts 53 and 54 will be movedtowards or away from each other for properly adjusting the contacts withrespect to the free end of the switch arm 5|. pivoted at 6| and 62.

A wire 63 connects the arm 58 with a movable contact 64 carried by anarm 65 pivoted at 53. A spring 61 tends to return the arm 65 to itsnormal horizontal position when the said arm has moved the contact 64away from the stationary The arms 56 and 58 are respectively contact SB.The last-mentioned contact is con- I nected by a wire '69 to the motor40.

A movable contact in is carried by an arm II which is pivoted at 12.This arm is normally maintained in a horizontal position by a spring isso that the contact 19 will engage a stationary contact l4 connected bya wire 15 with the arm 58.

A wire 16 connects the wire 46 with the reversing field of the motor 40and the wire 11 connects the reversing field with the arm 1| and,therefore, with the contact 10. I

The operation of my device is as follows: When the motor In is operatingunder a normal load .for operating the compressor or other instrumen- 45will pass through the arm 5|, the wire 63, the

movable contact 65, the stationary contact 61 and the wire 39 to themotor 49. Thereturn circuit is made through the wire 15 and the wire 46.The screw 42 will be revolved by the motor 40 and cause the threaded nut43 to be moved towards the contact 35 until the finger 65a connectedwith the nut 43 engages the contact 65 and moves it away from thecontact 33 thereby breaking the circuit to the motor 40. l

The members 65, 61, H and I4 constitute a limit switch which controlsthe operation of the motor 43 and stops said motor after the lever 29has been rocked sufllciently to move the slidable section 3| of thepulley to its inner or outer limits. The

stopping of the motor prevents the screw 42 from will be actuated at aslower speed.

On the other hand when the current falls in the primary coil 41 themember 49 will be moved outwardly from the secondary coil 43 and causethe arm 5| to be rocked towards the contact 53 until it engages saidcontact. At this time current from the wire 45 will. pass through thewire 15, contacts l4, l0 and wire 11 to the motor 40 whereby said motorwill be directly operated so that the screw 42 will move the nut 43towards the motor 40 while the slidable section 3| of the pulley will bemoved towards the section 32. As the section 3| moves towards thesection 32 the diameter of the pulley will be increased and. therefore,the compressor will be driven at a greater speed. 7

When the section 3| is moved towards the section 32 the finger 65a willmove towards the movable contact member H and when it engages saidcontact member it will move it outwardly whereby the contact in will bemoved away from the contact 14 and thus break the circuit to the motor40.

It will be seen by this construction that as the current drops from themotor circuit it will automatically cause the compressor to be runfaster and thus make the motor pull at its highest efllciency throughoutthe entire load, and, therefore, the load can be kept approximatelyconstant over the entire period of the operation.

The hinging of the motor I!) in connection with the lip Hi and springwill permit the motor ill to adjust itself when the pulley representedby the sections 3| and 32 present a larger.

or smaller diameter to the belt I8.

It will be noted at all times that when the current in the circuit ofthe motor l0 increases, it will cause the contact arm 5| to move againstthe contact wire to cause the small motor 40 to.

run in its normal direct rotation, while the reversing of the motorcaused by the decreasing current in the primary coil 41 will cause thearm 29 to be rocked in a direction whereby the section 3| of the pulleywill be moved toward th section 32 of the pulley, thus increasing thespeed of the compressor.

While a refrigerating machine has been referred to in the specificationand in the claims, it is to be understood that this device is notlimited to a refrigerating machine or air conditioning apparatus, sinceit can be employed in any apparatus where it is desired to maintain aconstant load on an electric motor due to varying operating conditionsrequired by the work.

I claim:

1. In an apparatus of the character Mcribed, a driven element, anelectric motor for operating the driven element, means for maintaining,the

load on the motor substantially constant at all times comprising amechanical transmission between the motor and the driven element, acircuit supplying current to the motor, means operating the transmissionfor causing an increase or decrease of the speed oi said driven element,a reversible motor actuating the operating means, a circuit branchingfrom the first circuit for supplying current to the reversible motor forcausing said motor to operate in one direction, a wire connected betweenthe branch circuit and the reversing field oi the second motor, atwo-way switch actuated by the reversible motor for alternately openingor closing the circuits to the reversible motor," and means operated inaccordance with current supplied to the first motor-for controlling thesupply oi current through the twoway switch to the second motor.

2. In an apparatus oi the character described, a driven element, anelectric motor ior operating the driven element, means for maintainingthe load on the motor substantially constant at all times comprising amechanical transmission between the motor and the driven clement, meansadjusting the transmission for varying the speed of the driven elementand including a reversible so 10 third circuits, and means operated inaccordance with fluctuations in' the circuit to the first motor forcontrolling operation 01' the second switch.

3. In an apparatus of the character described, a driven element, anelectric motor for operating 15 the driven element, means formaintaining the load on the motor substantially constant at all timescomprising a mechanical transmission between the motor and the drivenelement, a reversible motor, means between said motor and 20transmission and actuated by the reversible motor for operating thetransmission, a limit switch for controlling the operation of thereversible motor in either direction of rotation, a two-way switchcontrolling the fiow of current for direct 2s operation oi thereversible motor and for the revers rotation of said motor, and amagnetic means influenced by fluctuation in the current to the firstmotor for alternately operating the twoway switch.

' JOHN 1". MERCER.

